1. Field of the Invention
The present invention relates generally to medical dispensing devices and, more particularly, to recyclable dispensing devices that permit selectively measured dosages of a liquid to be dispensed.
2. Background of the Related Art
Patients suffering from diseases such as diabetes must inject themselves several times each day with an insulin solution. Since the volume of insulin solution to be injected varies from injection to injection, it is necessary for such patients to be able to measure a precise volume of insulin. Diabetics have conventionally used a syringe for injection of insulin. However, it is difficult to control the operation of the syringe as well as the quantity of drug injected.
In order to permit a diabetic to measure and administer a more accurate and controlled dosage, injector pens have been developed which enable a particular dosage to be accurately and conveniently measured. Generally, these pens are secured onto a cartridge having a particular quantity of liquid medication sealed therein. The cartridge includes a plunger and a mechanism for advancing the plunger in the cartridge in a manner to dispense the medication. Injector pens may be reusable or disposable. In reusable pens, a user can change a spent cartridge and reset the leadscrew of the pen back to its initial position. In a disposable pen, the cartridge is permanently captured in the pen which is disposed of after the contents of the cartridge have been exhausted.
One such disposable pen that has functioned very adequately is disclosed in U.S. Pat. No. 5,295,976. Specifically, a dispensing device is disclosed and includes an internally threaded collar and an externally threaded plunger rod. In order to set a dosage of medication to be delivered, the collar is rotated thereby causing displacement of the collar toward the proximal end of the injection device. Rotation of the collar causes the integral cap to become effectively displaced both rotationally and axially toward the proximal end of the pen. As this displacement occurs, the segment of the dose-indicating scale which is visible through a window varies to show a linear increase in the number to indicate an increased dosage of liquid to be dispensed. Once the desired dosage is selected, a force is applied to the end of the cap causing a linear displacement of the cap, integral plunger rod, and piston to dispense liquid from the container. The dispensing displacement of the plunger rod is halted by abutting contact between the cap and a stop element.
In U.S. Pat. No. 5,308,340, another recyclable injection device is disclosed. In particular, a plunger rod is received within the housing for exerting a force on a piston closing a second end of the container. The plunger rod has a noncylindrical cross section with a first surface including threads and a second surface which can, optionally, include a series of ratchet teeth. A collar is received within the housing adjacent the second end of the container for permanently retaining the container of liquid within the housing. The plunger rod passes through the noncylindrical opening in the collar and is prevented from rotating with respect to the housing by the collar. A hollow cap envelopes the plunger rod opposite the container of liquid. The skirt of the hollow cap extends inside the housing. The cap includes a threaded interior surface which movably engages the plunger rod for calibrated adjustment relative thereto. A stop is provided within the housing, and a distal facing surface is provided on the hollow cap for contacting the stop upon linear movement of the cap and plunger rod as a unit toward the container to dispense liquid therefrom. In operation, the cap is rotated in a counterclockwise direction causing the threads of the cap to travel along the threaded portion of the rod. This rotation does not cause displacement of the plunger rod with respect to the housing, but backs the distal end of the proximal cap portion away from a stop shoulder on the inside of the housing. When the cap has been positioned to the desired dosage, pressure is applied to the end of the cap for causing it to move linearly toward the distal end of the housing until a shoulder defined by a radially exposed portion of the distal end contacts a stop.
Finally, in U.S. patent application Ser. No. 08/399,764, the parent application to the present application, a medication dispensing device is disclosed which includes a dial telescopingly disposed within a housing wherein the dial can be engaged with a nut disposed on a lead screw. The lead screw, in conjunction with the dial and the nut, ultimately serves as a plunger to eject the medication from a cartridge contained within the device. If the dial is rotated while not engaging the nut, a dosage will not be set, and in order to commence an injection, a button assembly must be depressed relative to the dial to disengage the dial from the housing. The disclosure of U.S. patent application Ser. No. 08/399,764 is incorporated by reference herein.